1. Field of the Invention
This invention relates to a method for producing a plasticizer from the ester obtained by reacting phthalic anhydride with an alcohol having 4-18 carbon atoms in the presence of as a catalyst, a tetraalkyl titanate or a polymer thereof.
2. Description of the Prior Art
The esterification reactions using a tetraalkyl titanate as a catalyst are disclosed in Japanese patent publication No. 3806/1972, Japanese patent application laid-open No. 135911/1974, etc., but the resulting esters obtained according to these reactions are treated in the presence of water, and also such a treatment as blowing-in of steam is carried out for removing the catalyst, and hence the treatment of the esters have had a disadvantage in that the amount of water and the loss of heat energy are both large. Further since the acid value increases in the treatment of blowing-in of steam, there has been also a disadvantage in that addition of an alkali before or after the reactions is required. Further the resultant plasticizer have had a drawback in that the content of titanium therein was high and also the storing-stability was inferior.
U.S. Pat. Nos. 4,007,218 and 3,818,071 both disclose an alkaline treatment of esters prepared in the presence of a titanate catalyst.
With regard to the treatment of esters prepared in the presence of an acidic catalyst, Japanese patent publication No. 18027/1976 discloses a contact treatment of esters with an adsorbent obtained by adding a carrier to an aqueous solution of a carbonate or hydroxide of alkali metals or alkaline earth metals, followed by mixing treatment. Further, U.S. Pat. No. 3,717,672 discloses a treatment of phthalic esters by contacting the phthalic esters with dry slaked lime having associated therewith a very small proportion of an ionizing liquid such as water.
However, in any of these references, it is necessary to employ water or steam at the time of the treatment, and further the characteristic properties of the ester plasticizers such as acid value, color number, volume resisitivity, etc. are insufficient.
Recently, demand for no public nuisance, high quality product and energy saving in chemical industries is strong and plasticizer industry is not exceptional in these points. Accordingly, it is an important problem in producing ester plasticizers, to overcome the above-mentioned drawbacks accompanying the treatment.
It is an object of the present invention to provide a method which is able to overcome the above-mentioned difficult problem in general. It is another object of the present invention to provide a method for producing a plasticizer containing only a small content of titanium, without producing a large amount of waste water.
The method for producing a plasticizer according to the present invention is characterized in treating the ester obtained by reacting phthalic anhydride with an alcohol having 4-18 carbon atoms in the presence of a tetraalkyl titanate or a polymer thereof, with a solid alkali and adsorbing agent(s) in the absence of water.
The alcohols used in the method of the present invention are those having 4-18 carbon atoms and for example, 2-ethylhexanol, n-butanol, isobutanol, heptanol, nonanol, decanol, decyl alcohol and the like can be mentioned.
As tetraalkyl titanate, tetraisopropyl titanate, tetrabutyl titanate, tetraheptyl titanate, tetraoctyl titanate, tetraisodecyl titanate and the like can be mentioned.
The esters of the present invention can be obtained by adding an alcohol to phthalic anhydride and further adding a small amount of a tetraalkyl titanate or its polymer and carrying out the reaction at a high temperature of 150.degree. C. to 250.degree. C. in the atmosphere of an inert gas, taking out formed water to the outside of the system and after reducing the acid value down to 0.1 or less within 3 to 6 hours, and distilling off the alcohol in excess.
The method for producing a plasticizer of the present invention has a feature in the treatment of the above-mentioned ester with a solid alkali and adsorbing agent(s) in the absence of water. As the method for treating esters with a solid alkali and adsorbing agent(s), a method which relies on treating the ester with a solid alkali, followed by treatment with adsorbing agent(s), and a method in which the treatment is carried out with a mixture of a solid alkali and adsorbing agent(s), can be thought of. As the treatment with a solid alkali, there are a method in which an ester is stirred in a treating vessel with a powdered alkali and then an excessive alkali is removed, etc.
The solid alkali used in the method of the present invention, has no particular limitation so long as it is in solid state. Those of powdered form or granular form are preferable, and sodium carbonate, sodium bicarbonate, calcium carbonate, sodium hydroxide, potassium hydroxide, barium carbonate, etc. are useful, but sodium bicarbonate and sodium carbonate are preferable.
The amount of the solid alkali used has also no particular limitation so long as it is an equivalent amount or more to the acid value of the ester. Arbitrary selection is made according to the treating method, but a method in which an ester is contacted with a large excess of a solid alkali in a treating vessel and the excessive alkali is recovered by providing a solid-liquid separator or the like, is preferable. The recovered solid alkali can be used again. The treating temperature is in the range of 100.degree. C.-200.degree. C., preferably 150.degree. C.-200.degree. C., most preferably 170.degree. C.-200.degree. C. and the treating time is 0.5-4 hours.
The treatment of the ester having been treated with a solid alkali, with adsorbing agent(s) is carried out, for example, by adding activated clay with stirring, and then adding diatomaceous earth, followed by filtration. In this case, activated clay and diatomaceous earth are used in the amounts of 0.5-2.0 g and 0.1-1.0 g per Kg of the ester, respectively, aand the treatment is carried out at a temperature of 80.degree. C.-150.degree. C., preferably 80.degree. C.-100.degree. C. for 0.5-2.0 hours. As adsorbing agent(s) used, an activated charcoal can be mentioned in addition to the above-mentioned activated clay and diatomaceous earth. Further, if necessary, it is possible to carry out the alkali treatment and the adsorbing agent treatment simultaneously.
The characteristic feature of the production method of the present invention is that a step of blowing-in of steam, not to mention the water-washing step, is unnecessary and on this account, water, electric power and heat energy can be saved. Further the amount of waste water is exceedingly reduced and the quality of the waste water is improved. Further, the acid value and volume resistivity of resultant plasticizers are superior to those of conventional plasticizers. Further the fact that titanium content is extremely small and preservation stability is good, is also the advantage of this invention.